Rewrite Obj-C workflow in Rust

This is functionally equivalent to the previous workflow_objc, with the
following changes:
1. It mutates the `core.function.metaAnalysis` workflow rather than
   registering a new named workflow. The activities now all check for
   the presence of the Objective-C metadata added by `ObjCProcessor` to
   determine whether they should do work, rather than relying on
   `MachoView` to override the function workflow when Objective-C
   metadata is present. This fixes
   https://github.com/Vector35/binaryninja-api/issues/6779.
2. The auto-inlining of `objc_msgSend` selector stub functions is
   performed in a separate activity from the processing of
   `objc_msgSend` call sites. The selector stub inlining activity is
   configured so that it does not run in `DSCView` as the shared cache
   needs different behavior for stub functions more generally that
   `SharedCacheWorkflow` already provides.
3. The way that types like `id` and `SEL` are referenced is fixed so
   that they show up as `id` rather than `objc_struct*`.

This also replaces the Objective-C portion of the shared cache's
workflow, and incorporates several bug fixes that had been applied to it
but not the standalone Objective-C workflow.